If you think your partner is deceptive and have collected evidence against them, your next step will be the most difficult of all: you will have to deal with it.
If you still don't know if a business is going on, you should be careful and ask first where it was and what it did. If you don't have undeniable evidence that they're behind your back, you don't want a full confrontation.
Think of it as an all or nothing situation. If you don't have enough evidence, not only will you let them know you know it, but you will probably look a bit silly. If you pay attention to your understanding, it will be much more difficult to collect evidence for the future. In other words, don't show them your hand until you're ready.
I believe this book will help you to get started and hopefully take you all the way, I wish you success.

Karlek Diaz.